The invention relates to a method of shutting down an internal combustion engine, particularly a motor vehicle internal combustion engine.
The shut down of an internal combustion engine of a motor vehicle is usually initiated by the driver using the ignition key. Turning the ignition key generally cuts off the fuel supply, that is, the injection valves or injectors are de-energized. In the case of stop-start operation the shut down of the internal combustion engine is initiated by the engine management system, once certain conditions such as a zero vehicle speed and an actuation of the brake of the motor vehicle are fulfilled.
When an internal combustion engine is switched on—by the driver turning the ignition key or by the engine management system in stop-start operation of the internal combustion engine—with electronically controlled ignition and/or injection, there is the problem that the actual position of the internal combustion engine, that is to say the angular position of the crankshaft and the camshaft and hence the cylinder position are initially unknown. Only once the shafts of the internal combustion engine are turning do the assigned sensors deliver analyzable output signals, from which it is possible to determine the instantaneous position of the crankshaft and the camshaft. Only when certain engine-specific conditions are fulfilled and the reference mark on the crankshaft sensor wheel is recognized can synchronization take place, in which the correct angular position of the crankshaft and the camshaft is detected and in which the correct cylinder positions are therefore also known.
When starting an internal combustion engine from different positions of the crankshaft the starting time can vary considerably. There are especially unfavorable and especially favorable positions. In the most unfavorable case, for example, a four-cylinder, four-stroke engine needs approximately 180° more rotation of the crankshaft for starting of the internal combustion engine than in the most favorable position. The instant start up of a spark ignition engine is only possible if the crankshaft happens by chance to have attained the necessary starting position for instant starting.
Various approaches to a solution of this problem are disclosed by the state of the art.
Thus DE 198 58 992 A1, for example, describes a starting/drive unit for an internal combustion engine of a motor vehicle, in which the actual process of starting the internal combustion engine is preceded by a starting clarification phase, in which the starting conditions are detected with the clutch engaged and a decision is made with regard to the ensuing operating phase. This starting clarification phase is intended to permit starting of an internal combustion engine without the usual starter.
A further approach to solving the problem outlined above consists in actively positioning the crankshaft upon shut down of the internal combustion engine of a motor vehicle. DE 198 35 045 C2, DE 199 36 885 C2 and DE 199 60 984 A1, for example, disclose various methods for actively controlling the process of shutting down an internal combustion engine, in which the crankshaft is stopped in a defined angular position, which corresponds to the most favorable starting position of the internal combustion engine. Stopping the crankshaft in a specific angular position is achieved, according to DE 198 35 045 C2 for example, by means of a braking system, in the case of DE 199 36 885 C2 by means of an electric motor for generating a brake torque, and in the case of DE 199 60 984 A1 by an exhaust valve control system.
Alternatively it is also possible to move the crankshaft into a desired angular position during or after the shut down of the internal combustion engine. DE 100 30 001 A1 discloses a method for the controlled shutting down of an internal combustion engine, in which the crankshaft is moved into the desired angular position after completion of the shutdown process; DE 100 50 170 A1 describes a method in which means of braking or driving bring the crankshaft into a predefined rest position during the process of shutting down the internal combustion engine.
Such methods in which the crankshaft is actively positioned during the process of shutting down the internal combustion engine are only feasible, however, in connection with some but not all starting systems.
For the sake of completeness, reference is also be made to DE 197 35 455 C1, which discloses a method which actively intervenes in the process of shutting down an internal combustion engine in order to reduce exhaust emissions. However, this active intervention in the shutting down process does not have any direct influence on the rest position of the crankshaft.
Based on the aforementioned state of the art, it is the object of the present invention to provide a method of shutting down an internal combustion engine in such a way that the engine starting time during the subsequent starting process of the internal combustion engine is significantly reduced regardless of the starting system.